Question about ViewEngines.Engines.FindView method and the masterName parameter - asp.net-mvc

Question

This method works great if I pass null to the last param masterName, My views setup in my class derivved from RazorViewEngine work and all is good. Out of curiosity what is the masterName parameter used for? I first thought maybe it was for a layout.cshtml, however; when I pass it a layout it throws an exception.... Any ideas on how this is supposed to be used, what is it looking for?
Custom View Engine (Hardly LOL)
public class CustomRazorViewEngine : RazorViewEngine
{
private readonly string[] NewViewFormats = new[]
{
"~/Views/Messaging/{0}.cshtml"
};
public CustomRazorViewEngine()
{
base.ViewLocationFormats = base.ViewLocationFormats.Union(NewViewFormats).ToArray();
}
}
public string RenderViewToString(string viewName, object model, ControllerContext controllerContext,
string masterName)
{
if (string.IsNullOrEmpty(viewName))
viewName = controllerContext.RouteData.GetRequiredString("action");
controllerContext.Controller.ViewData.Model = model;
using (var stringWriter = new StringWriter())
{
ViewEngineResult viewEngineResult = ViewEngines.Engines.FindView(controllerContext, viewName, masterName);
var viewContext = new ViewContext(controllerContext, viewEngineResult.View,
controllerContext.Controller.ViewData,
controllerContext.Controller.TempData,
stringWriter);
viewEngineResult.View.Render(viewContext, stringWriter);
return stringWriter.GetStringBuilder().ToString();
}
}

Answer 1

So after some more debugging I have found what appears to be the correct answer. First let me state that the masterName parameter is the name of the "Layout" so to say that the view being rendered will use. The catch here is that layout must be able to be located. So instead of the code for the ViewEngine in my original post the following code works as desired.
public string RenderViewToString(string viewName, object model, ControllerContext controllerContext,
string masterName)
{
if (string.IsNullOrEmpty(viewName))
viewName = controllerContext.RouteData.GetRequiredString("action");
controllerContext.Controller.ViewData.Model = model;
using (var stringWriter = new StringWriter())
{
ViewEngineResult viewEngineResult = ViewEngines.Engines.FindView(controllerContext, viewName, masterName);
var viewContext = new ViewContext(controllerContext, viewEngineResult.View,
controllerContext.Controller.ViewData,
controllerContext.Controller.TempData,
stringWriter);
viewEngineResult.View.Render(viewContext, stringWriter);
return stringWriter.GetStringBuilder().ToString();
}
}
public class CustomRazorViewEngine : RazorViewEngine
{
private readonly string[] NewMasterViewFormats = new[]
{
"~/Views/Messaging/Layouts/{0}.cshtml"
};
private readonly string[] NewViewFormats = new[]
{
"~/Views/Messaging/{0}.cshtml"
};
public CustomRazorViewEngine()
{
base.ViewLocationFormats = base.ViewLocationFormats.Union(NewViewFormats).ToArray();
base.MasterLocationFormats = base.MasterLocationFormats.Union(NewMasterViewFormats).ToArray();
}
}
Now when calling
string returnViewToString = _viewUtils.RenderViewToString("RegistrationEmail", new RegistrationEmailModel
{ UserName = userName
},
this.ControllerContext,"_RegistrationEmailLayout");
Everything is happy and my layout for the passed in view, if it exists in the folder gets used. This was the highlight of my day... LOL